Important Safety Alerts

Medical device manufacturer, Biomerieux, has issued a field safety notice concerning Mueller Hinton 2 Agar with reference number 43301, 43302, 43309, 43511, 41864 and 51075.

The manufacturer's internal studies have shown that some strains of Staphylococcus aureus with a low level resistance to methicillin may be not detected when tested on Mueller Hinton 2 by using a cefoxitin disk and whatever the standards used.

The two potential risks associated with this issue are as follows:

• Susceptibility testing of a clinical isolate (diagnosis of infection): The non-detection of MRSA corresponds to a false sensitive result for the given antibiotic. Then, the risk is to prescribe an antibiotic that will not be efficient (inappropriate treatment) and to delay the correct treatment.
• Confirmation of methicillin resistance when MRSA has been isolated during a screening process: This is a confirmation of a positive screening test. So, a false negative test will alert the microbiologist and will lead to additional testing because the false negative result (obtained with the Mueller Hinton 2 medium) will be in discordant with the first screening positive result (usually obtained with a screening medium as chromID MRSA).

In parallel, the manufacturer has developed a Mueller Hinton E (MHE) medium which is compliant with the European Committee on Antibiotic Susceptibility Testing (EUCAST) and the Clinical and Laboratory Standards Institute (CLSI) standards. This new medium allows methicillin-resistant Staphylococcus aureus (MRSA) detection even for the isolates expressing resistance at low level and whatever the genotype is (mecA or mecC). Therefore, based on the internal studies, the manufacturer strongly advises users to use Mueller Hinton E in replacement of Mueller Hinton 2 agar.

In parallel, the manufacturer has developed a Mueller Hinton E (MHE) medium which is compliant with the European Committee on Antibiotic Susceptibility Testing (EUCAST) and the Clinical and Laboratory Standards Institute (CLSI) standards. This new medium allows methicillin-resistant Staphylococcus aureus (MRSA) detection even for the isolates expressing resistance at low level and whatever the genotype is (mecA or mecC). Therefore, based on the internal studies, the manufacturer strongly advises users to use Mueller Hinton E in replacement of Mueller Hinton 2 agar.

In the case users would not being able to use the Mueller Hinton E and if they are using the CA‐SFM 2013 guidelines for MRSA detection, the manufacturer advises users to test by an alternative method all the isolates that have a cefoxitin inhibition zone falling between 25 and 29 mm. If the inhibition zone is ≥ 30 mm, users do not need to confirm with other tests.

In the case users are using the EUCAST or the CLSI standard, the manufacturers advises users not to use Mueller Hinton 2 agar anymore for MRSA detection purpose.

In addition, the manufacturer recommends users to discuss with their Laboratory Directors to evaluate the impact and determine if any retrospective analysis of results is required.

According to the local supplier, the affected products were distributed in Hong Kong.

If you are in possession of the products, please contact your supplier for necessary actions.

Posted on 11 April 2014